Author:

Takasada Shibauchi(Department of Physics, Kyoto University)

In high temperature superconductivity,
charge doping is a natural tuning parameter
that takes copper oxides from the antiferromagnet
through the superconducting `dome'-shaped region.
In the metallic state above $T_{\rm c}$ the standard Landau's
Fermi-liquid theory of metals, as typified by the temperature squared
($AT^2$) dependence of resistivity, appears to break down.
The expected recovery of the usual Fermi-liquid
metal on the high doping side is fundamental but ill understood.
Here we uncover a new transformation in an overdoped
superconducting copper oxide Tl$_2$Ba$_2$CuO$_{6+x}$ from the
non-Fermi to
a Fermi-liquid state driven by magnetic field [1].
From the
$c$-axis resistivity measured up to 45~T,
we show that the
Fermi-liquid $AT^2$ features, accompanied by a
field-linear magnetoresistance,
appear above a field $H_{\rm FL}$. This crossover field $H_{\rm
FL}$ decreases linearly with decreasing temperature $T$ and lands
at a quantum critical point (QCP) near the
upper critical field $H_{\rm c2}(0)$.
The Fermi-liquid coefficient $A(H)$ shows a power-law diverging
behavior on the approach to the QCP, indicating the second-order
quantum phase transition at this field. The connection between
the field-induced QCP and the pseudogap observed in the
underdoped regime will be discussed.
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[1] T. Shibauchi {\it et al.}, Proc. Natl. Acad. Sci. USA {\bf
105}, 7120 (2008).

To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2009.MAR.B2.4